Add Js.Bigint.

Author: cristianoc

jscomp/main/builtin_cmi_datasets.ml

@@ -282,6 +282,9 @@ module Float = Js_float
 module Int = Js_int
 (** Provide utilities for int *)
 
+module Bigint = Js_bigint
+(** Provide utilities for bigint *)
+
 module Option = Js_option
 (** Provide utilities for option *)